1. Field of the Invention
The present invention relates to a sheet feeding apparatus for feeding a sheet and a control method thereof, and a document reading apparatus for reading information on a document as a sheet.
2. Description of the Related Art
FIG. 9 shows a schematic structure of a conventional document reading apparatus 1′. Note that since a principal structure will be explained by denoting the same components by the same reference numerals in embodiments, only required portions will be mentioned. Referring to FIG. 9, a feed roller 3 feeds, onto a conveying path RT, a lowermost sheet S1, which is separated one by one from a document bundle S placed on a feed tray 4 by a separation roller 5 that rotates in a direction opposite to the feed roller 3 while being in pressure-contact with the feed roller 3. On the conveying path RT, image reading units 6a and 6b are disposed, and read information on the sheet S1, which is conveyed by a pair of upstream-side conveying rollers 11a and 11b and a pair of downstream-side conveying rollers 12a and 12b. 
Japanese Patent No. 3677356 discloses an arrangement in which a movable guide is disposed outside the outer surface of a feed roller, so as to prevent leading ends of documents from contacting the feed roller upon setting documents.
In the conventional document reading apparatus 1′, when the document bundle S is set on the feed tray 4, the feed roller 3 is partially exposed from the upper surface of the conveying path RT. This is because even a document with folds can be surely gripped and conveyed by the feed roller 3. For this reason, the leading end portion of the lowermost sheet S1 abuts against the outer surface of the feed roller 3 to stop its forward movement, so as to set a state in which upper documents approach a pressure-contact surface (nip) between the feed roller 3 and separation roller 5 (to be referred to as an inversely aligned state). When feeding operations are continued in the inversely aligned state, since an upper document is picked up earlier, so-called multi-feeding (a plurality of documents are fed simultaneously without separating the document bundle S one by one) tends to occur.
In Japanese Patent No. 3677356 above, in order to prevent the inversely aligned state, the movable guide is used to prevent the leading end portions of documents from contacting the feed roller upon setting the documents. However, documents such as four-folded documents with central folds abut against the feed roller to cause the inversely aligned state.
Note that the aforementioned problem is posed not only in the document reading apparatus but it may be similarly posed in a sheet feeding apparatus which separates and feeds sheets.